The invention relates to an actuator which may find application in a cab tilting apparatus of a cab-over, large-sized vehicle, for example.
In a large-sized truck of cab-over type, an engine room is disposed underneath a driver's platform which is commonly referred as a cab, and a cab tilting apparatus is provided to lift the cab to its forwardly tilted position so that the maintenance and inspection of an engine and associated parts located within the engine room may be made.
It is generally necessary that the cab tilting apparatus be associated with a mechanism which prevents a falling down of the cab under gravity when an output rod is raised and is brought to a halt with a cab assuming a forwardly tilted position and which also prevents the cab from turning over in the forward direction in the event the cab is further caused to tilt forwardly until its center of gravity moves beyond the tilt axis (fulcrum). Such mechanism conventionally comprises as an electromagnetic brake of a worm gear which can be self-locked. When an electromagnetic brake is used as a stop for the actuator which is subject to both tensile and compressive loads, an increased cost results disadvantageously. The use of a worm gear suffers from a low mechanical efficiency, disadvantageously requiring a motor of an increased capacity.